1. Field of the Invention
The present invention relates to a servo control apparatus and a gain adjusting method. More specifically, the present invention relates to a servo control apparatus and a gain adjusting method which determines a gain of a focus servo loop or a tracking servo loop of a disk apparatus, for example.
2. Description of the Prior Art
One example of such a kind of servo control apparatus is disclosed in, for example, Japanese Patent Laying-open No. 5-217315 [G11B 21/10, G11B 7/09] laid-open on Aug. 27, 1993. As shown in FIG. 10, in this servo control apparatus 1, a gain automatic adjusting system 2 produces a sine wave in a VCO calculating portion (VCO) 3, and adds it to an addition point 5 in a state where a servo loop is closed. Furthermore, by passing an output of a servo operation portion 4 through a band-pass filter portion (BPF) 6 only a required frequency component is extracted, and the required frequency component is multiplied with the sine wave from the VCO calculating portion 3 in a multiplication portion 7. Then, a multiplied output is applied to a notch filter portion (NFT) 8, and its unnecessary frequency component is removed, and a gain of the servo operation portion 4 is increased or decreased in a gain calculating portion 9 in such a manner that the multiplied output becomes a predetermined value.
In this prior art, however, in the gain calculating portion 9, a value of a variable LSTEP is changed, and the gain is increased or decreased by the variable LSTEP, and the variable LSTEP is changed by a dichotomizing method so as to gradually decrease a varying width (increase or decrease) of the gain, and thus, the number of adjustment times (increase or decrease) becomes large, and therefore, it requires a long time until an appropriate gain is adjusted.
Therefore, it is a primary object of the present invention to provide a servo control apparatus and a gain adjusting method of a servo loop, which is capable of adjusting a gain in a short time.
The present invention is a servo control apparatus which determines a reproduction gain of a focus servo loop or a tracking servo loop of a disk apparatus, and comprises: a phase difference detecting means for detecting a phase difference between an input sine wave and a sine wave being fed-back; an adjusting means for adjusting a loop gain of a servo loop to determine the reproduction gain according to the phase difference; a generating means for generating a correlation signal correlated with the phase difference at every time that the loop gain is adjusted by the adjusting means; a determining means for determining whether or not a DC component of the correlation signal generated by the generating means exceeds a predetermined threshold value; an adjusting amount setting means for setting an adjusting amount of the loop gain to a first predetermined amount when it is determined that the DC component of the correlation signal exceeds the predetermined threshold value, and setting the adjusting amount to a second predetermined amount smaller than the first predetermined amount when it is determined that the DC component of the correlation signal is equal to or smaller than the predetermined threshold value; a polarity detecting means for detecting a polarity of the DC component of the correlation signal generated by the generating means; a polarity comparing means for comparing the polarity of this time detected by the polarity detecting means and the polarity of last time; and a gain determining means for determining the loop gain adjusted last time or the loop gain adjusted this time as the reproduction gain when a comparing result of the polarity comparing means indicates a reverse in polarity and also the second predetermined amount is set.
In an aspect, the present invention is a servo control apparatus which determines a reproduction gain of a focus servo loop or a tracking servo loop of a disk apparatus, and comprises: a phase difference detecting means for detecting a phase difference between an input sine wave and a sine wave being fed-back; an adjusting means for adjusting a loop gain of a servo loop to determine the reproduction gain according to the phase difference; a determining means for determining whether or not a DC component of a correlation signal correlated with the phase difference exceeds a predetermined threshold value; and an adjusting amount setting means for setting an adjusting amount of the loop gain in response to a determining result of the determining means.
The present invention is a gain adjusting method in a servo control apparatus which determines a reproduction gain of a focus servo loop or a tracking servo loop of a disk apparatus, comprising following steps of: (a) detecting a phase difference between an input sine wave and a sine wave being fed-back; (b) generating a correlation signal correlated with the phase difference; (c) determining whether or not a DC component of the correlation signal exceeds a predetermined threshold value; and (d) adjusting a loop gain of a servo loop for determining the reproduction gain with a first predetermined amount when it is determined that the DC component of the correlation signal exceeds the predetermined threshold value, and adjusting the loop gain with a second predetermined amount smaller than the first predetermined amount when it is determined that the DC component of the correlation signal is equal to or less than the predetermined threshold value.
The servo control apparatus is adapted to a disk apparatus which reproduces an optical disk such as a CD, a DVD, and etc., for example, and determines a reproduction gain of a servo loop (servo loop for reproduction) such as a focus servo loop and a tracking servo loop. In the servo control apparatus, for example, a sine wave of a predetermined frequency (target frequency) is input as a disturbance. The sine wave is superposed on a focus control voltage or a tracking control voltage applied from a pick-up as an input signal (feedback signal), and applied to the pick-up after being subjected to a phase compensation or a gain compensation. The feedback signal is filtered a band-pass filter (BPF) having a center frequency being set to the target frequency, and a component of the target frequency is extracted. That is, a sine wave which is fed-back is obtained.
The phase difference detecting means detects a phase difference between the sine wave of the target frequency and the sine wave being fed-back. The gain adjusting means adjusts a loop gain of a servo loop (servo loop for determination) for determining a reproduction gain of the servo loop for reproduction in accordance with the phase difference. More specifically, a correlation signal correlated with the phase difference is generated at every time that the loop gain is adjusted, and it is determined whether or not a DC component of the correlation signal exceeds a predetermined threshold value. If the DC component of the correlation signal exceeds the predetermined threshold value, the loop gain is adjusted (increased or decreased) with a first predetermined amount set by the adjusting amount setting means. On the other hand, if the DC component of the correlation signal is equal to or less than the predetermined threshold value, the loop gain is increased or decreased with a second predetermined amount smaller than the first predetermined amount set by the adjusting amount setting means. That is, the loop gain is increased or decreased in such a manner that the DC component of the correlation signal is rendered 0 level (control target value), and in a case that the DC component of the correlation signal is greatly distant from the 0 level, the loop gain is increased or decreased by an adjusting amount of the first predetermined amount, and in a case that the DC component of the correlation signal becomes closer to a vicinity of the 0 level, the loop gain is increased or decreased with the second predetermined amount.
While the loop gain is thus adjusted, a polarity of the DC component of the correlation signal is detected by the polarity detecting means for each time that the correlation signal is generated. Furthermore, a comparison is made by the polarity comparing means between the polarity of the DC component of the correlation signal detected this time and the polarity of the DC component of the correlation signal last time, and if a comparison result indicates a reverse in polarity and also the adjusting amount of the loop gain is the second predetermined amount, a reproduction gain of the servo loop for reproduction is decided to the loop gain adjusted last time by the gain determining means or the loop gain adjusted this time. That is, in a case that the polarity of the DC component of the correlation signal becomes a reverse polarity depending upon before or after the gain adjustment, it is possible to say that the DC component of the correlation signal crosses the 0 level (control target value), and therefore, the DC component is the closest to the 0 level if the loop gain before or after the gain adjustment is set into the servo loop for reproduction. Therefore, the loop gain adjusted last time or the loop gain adjusted this time is determined (adopted) as the reproduction gain.
According to the present invention, in a case that the DC component of the correlation signal is more than the predetermined threshold value, the gain is greatly increased or decreased, and in contrary, if the DC component is equal to or less than the predetermined threshold value, an increasing or decreasing width of the gain is rendered small, and accordingly, it is possible to adjust the gain within a short time.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.